ALLUVIAL FACIES AND FACIES ASSOCIATIONS WITHIN THE LATE CRETACEOUS PRINCE CREEK FORMATION, NORTH SLOPE, ALASKA

Primary facies of the Late Cretaceous Prince Creek Formation of Alaska include fine-to medium-grained sandstone, very-fine to fine-grained rooted sandstone, rooted siltstone, carbonaceous shale, rooted mudstone, and coal. Bentonites and tuffs are also present but rare. Preliminary analysis suggests that these facies may be combined into four major facies associations based on vertical/lateral relationships.

Facies Association I (Meandering Channel Facies Association) is dominated by fine-to medium-grained crossbedded sandstone with minor rippled siltstone, carbonaceous shale, and mudstone. Sandbodies are laterally extensive sheets containing mud rip-up clasts, wood impressions, carbonized plant fragments, and bone. High width/depth ratios, multi-storied fining upward successions, basal erosion surfaces with pebble lags, and lateral accretion are characteristic of this facies association interpreted as meandering channel deposits.

Facies Association II (Anastomosed Channel Facies Association) is composed primarily of very-fine to fine-grained rippled sandstone with ubiquitous carbonized root traces. Finer-grained rippled/rooted siltstones and rooted mudstones suggestive of levees and paleosols are often found proximal to or overlying the sandbodies. Sandbodies are laterally restricted ribbons with low width/depth ratios that frequently exhibit basal erosion surfaces lacking basal lags. Accretion is primarily vertical and rarely lateral. Plant fragments, wood impressions, and siderite are common in this facies association interpreted as the deposits of anastomosed streams.

Facies Association III (Crevasse Facies Association) contains predominantly fine-grained rippled sandstone and siltstone with minor mudstone. Sandbodies are lobate in cross section. Basal contacts are primarily sharp to gradational, often with underlying finer-grained floodplain facies. Both fining upward and coarsening upward successions are evident. Carbonized root traces, plant fragments, and wood impressions are abundant in these crevasse deposits.

Facies Association IV (Floodplain Facies Association) consists of fine-grained facies including rooted siltstone, mottled/rooted mudstone, carbonaceous shale, and coal interpreted as paleosols, backswamps, lakes, and distal splays.